Nutrient subsidies in the coastal margin: implications for tree species richness and understory composition

dc.contributor.authorMiller, Rebecca
dc.contributor.supervisorStarzomski, Brian M.
dc.date.accessioned2019-05-01T23:05:12Z
dc.date.available2019-05-01T23:05:12Z
dc.date.copyright2019en_US
dc.date.issued2019-05-01
dc.degree.departmentSchool of Environmental Studiesen_US
dc.degree.levelMaster of Science M.Sc.en_US
dc.description.abstractThe subsidized island biogeography hypothesis proposes that nutrient subsidies, those translocated from one ecosystem to another, can indirectly influence species richness on islands by directly increasing terrestrial productivity. However, the lack of a formal statistical model makes it difficult to assess the strength of the hypothesis. I created a formal subsidized island biogeography model to determine how nutrient subsidies, in addition to area and distance from mainland, influence tree species richness. My model showed that an increase in terrestrial nitrogen abundance results in a decrease of tree species richness. Soil and plant δ 15N values were higher than expected and it is likely that nutrient subsidies from the marine environment are responsible for 15N enrichment. However, the range of observed nitrogen abundance is similar to inland coastal-zone forests, indicating that islands are similarly nitrogen deprived and may not be receiving enough nutrient subsidies to alter productivity. Tree species decline may therefore be more strongly related to the environmental conditions leading to patterns of nitrogen abundance rather than the abundance of nitrogen itself. Additionally, I proposed that bald eagles (Haliaeetus leucocephalus) are vectors of nutrient subsidies, depositing nutrient-rich guano at nest sites, which could alter soil chemistry and vegetation composition. In an exploratory study of seven nest sites, I found higher soil phosphorous at eagle nest sites relative to control sites (~ 33% higher). Phosphorous is a limiting nutrient in coastal temperate forests, additions help to alleviate chlorosis and slow growth especially when paired with nitrogen. Higher potassium concentration also occurred on eagle-inhabited islands but was not associated specifically with current nest sites, perhaps reflecting differential persistence of macronutrients in the soil. Despite expectations, soil δ 15N abundance was not statistically higher at eagle nest sites. Total soil nitrogen was also not statistically higher at eagle nest sites. There were no significant differences between vegetation composition at eagle nest sites and reference sites, but reference sites tended to be dominated by shrub species. Additionally, I proposed that bald eagles (Haliaeetus leucocephalus) are vectors of nutrient subsidies, depositing nutrient-rich guano at nest sites, which could alter soil chemistry and vegetation composition. In an exploratory study of seven nest sites, I found higher soil phosphorous at eagle nest sites relative to control sites (~ 33% higher). Phosphorous is a limiting nutrient in coastal temperate forests, additions help to alleviate chlorosis and slow growth especially when paired with nitrogen. Higher potassium concentration also occurred on eagle-inhabited islands but was not associated specifically with current nest sites, perhaps reflecting differential persistence of macronutrients in the soil. I expected to observe elevated nitrogen isotope signatures (δ 15N) given bald eagles’ position in the trophic web and the potential for volatilization of guano but soil δ 15N abundance was not statistically higher at eagle nest sites. Total soil nitrogen was also not statistically higher at eagle nest sites. There were no significant differences between vegetation composition at eagle nest sites and reference sites, but reference sites tended to be dominated by shrub speciesen_US
dc.description.scholarlevelGraduateen_US
dc.identifier.urihttp://hdl.handle.net/1828/10831
dc.languageEnglisheng
dc.language.isoenen_US
dc.rightsAvailable to the World Wide Weben_US
dc.subjectecosystem subsidiesen_US
dc.subjectbald eagleen_US
dc.subjectsubsidized island biogeographyen_US
dc.subjecttree diversityen_US
dc.subjectspecies-area curveen_US
dc.subjectcoastal foresten_US
dc.subjectisland biogeographyen_US
dc.subjectnitrogen isotopeen_US
dc.titleNutrient subsidies in the coastal margin: implications for tree species richness and understory compositionen_US
dc.typeThesisen_US

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